Containers for the storage and/or the transportation of pressurized or compressed gases and cryogenic gases have traditionally been made of metal. Metal was the material of choice because of its strength and its gas barrier properties. Some such tanks, known as "bottles", are currently used for the transportation and the storage of gases such as those used in hospitals or by welders. These bottles usually weigh about 150 pounds empty and only contain about 10 pounds of gas when filled. Accordingly, the transportation costs of gases in such bottles are high. Moreover, handling of these bottles frequently results in back strain and broken feet.
Metal lined-fiber wrapped containers were subsequently developed in conjunction with the space exploration program. These containers reduced the amount of metal required to contain the compressed or cryogenic gas. These containers utilize a gas impermeable metal, inner liner and a structural overwrap which is made of a composite material (i.e., fibers cured within a matrix resin). These containers are typically manufactured in cylindrical or spherical forms. Further information about metal lined-fiber wrapped containers may be found in the following publications, which are incorporated herein by reference: "Composite Cylinders for CNG", 36th Annual Conference, Reinforced Plastics/Composites Institute, The Society of the Plastics Industry, Inc., Feb. 16-20, 1981, Session 22-E, P. 1-8; Morris, E.E., "Advances in Composite Fiber/Metal Pressure Vessel Technology", American Institute of Aeronautics and Astronautics, Inc., 1989, p. 1-9; Morris, V.L., "Advanced Composite Structures For Cryogenic Applications", 34th International SAMPE Symposium, May 8-11, 1989, p. 1867-1876.
These containers find their application in specialized areas where the need to minimize container weight overshadows container cost. Such applications include: breathing systems for rescue backpacks, underwater diving, and mountain climbing; inflation systems for aircraft and life rafts; storage and transportation of pressurized and/or cryogenic gases for spacecraft, aircraft, and military applications.
Within the genus of metal lined-fiber wrapped containers, two species exist: a filament reinforced metal pressure vessel, and a metal-lined filament wound pressure vessel. These distinct vessels can be distinguished on a weight basis. In the former, weight bows to cost. The former has a load bearing metal liner. This means a thick metal, inner liner and a filament overwrap that reinforces the strength of the liner. In the latter, cost bows to weight. This means a thin metal liner which is sufficiently thick to provide adequate gas impermeability and a filament overwrap that provides the strength to withstand the internal gas pressure of the container.
The metals used for the above-mentioned liners are alloys of aluminum, stainless steel, and titanium or alloys such as Inconel or Monel. The continuous filaments (or structural fibers) used in the overwrap are fiberglass, aramid fibers, alumina fibers, boron fibers, and carbon fibers. The matrix resins used to cure or to consolidate the filaments of the overwrap are thermosetting and thermoplastic resins. Thermosetting resins, however, are the most popular and include epoxy, polyester, phenolic, bismaleimide, and polyimide resins.
The metal liner may be formed into the desired shape using conventional techniques. The structural overwrapping is wound over the metal liner, which acts as a mandrel, by a filament winding process. Filament winding, a well known process, consists of wrapping continuous fibers around a mold or a mandrel surface in precise geometric patterns, e.g. polar, helical, or hoop windings and curing or consolidating the wound fibers into a composite material. By properly orienting and proportioning one or more winding patterns, an efficient structure results in which filaments can be more uniformly loaded than with other methods of composite manufacture such as hand lay-up, tape laying or braiding.
In yet another lightweight container, thin metal foils or films are laminated onto films or fiber mats of polymers or glass and are used as the inner liner of the container. See U.S. Pat. Nos. 3,535,179 and 3,929,247 and French Patent No. 2,303,230. The metal foil acts as the gas impermeable barrier.